High current (800 to 6,000 ampere) electrical installations usually have one or more main bus bars with terminal ends that are provided with plural holes for connecting smaller feeder buses or electrical cables (conductors) to the main bus. The overall width of such a main bus typically is in a range of three and one-half to six inches. In the past, the patterns and spacings of these mounting holes or apertures used to affix electrical connection lugs to the main bus were determined solely by the manufacturers or designers of the electrical installations; variation was prevalent. This situation was changed by the National Electrical Manufacturers Association (NEMA), when it adopted a standard pattern comprising four mounting holes of 9/16 inch diameter centered at the corners of a square having sides of 1.75 inch length, as shown in FIG. 1. This NEMA standard for electrical connection lug mounting holes is used with half inch diameter mounting bolts. It is used on most high current switches.
An electrical connector lug having a single mounting hole, used in conjunction with just one of the bus mounting apertures, is the least expensive way to make electrical connections to a bus having mounting apertures arranged in the NEMA standard pattern, FIG. 1. But because such one-hole lugs are held in place by only one bolt, they can turn; they may thus become misaligned or even cause the secondary conductor to engage some component at a different electrical potential. The problems are substantial and potentially catastrophic. Consequently, many codes and standards prohibit the use of one-hole connection lugs without some means to prevent the lugs from turning. An obvious solution, of course, is to use two-hole lugs, as shown in FIG. 2. But this is a limiting arrangement; only two such connector lugs can be arranged side-by-side on a bus having the NEMA standard four-hole pattern, and the bus terminal requires twice as many bolts, nuts, and washers as are needed for one-hole lugs. The industry has not generally used two-hole connection lugs. Turn prevention clips, as illustrated in FIG. 3, have sometimes been used, but they have all of the disadvantages of two-hole connection lugs (FIG. 2) plus higher cost and poor appearance.
Turn prevention connection lugs as shown in FIG. 4 have been and are available; they have most frequently been utilized in mass produced products. The principal problem is that the dimension D may vary considerably, depending on the overall arrangement of the terminal portion of the main bus, so that a substantial number of different connector lugs is needed. Thus, these specialized connection lugs are not practical except in high volume applications. Of course, pins or nubs can be included in a terminal portion of a main bus, as shown in FIG. 5. But this makes it difficult or impossible to interconnect adjacent bus sections; the terminal portion of a main bus equipped with such pins is usually suitable only for cable connections. And additional costs can be substantial. Then too, a small hole through the connector lug aligned with a similar hole in the bus, and a pin in these holes, will prevent the lug from turning; see FIG. 6. This expedient has been and is used, but it requires two drilling operations and installation of a turn prevention pin for each connector lug, a lot of work and a lot of cost. Finally, multi-conductor terminals can be substituted for individual connector lugs, but this expedient is also unduly expensive.